1. Field of the Invention
The present invention relates to a drive unit equipped on a motion mechanism such as, for example, a machine tool or industrial robot, which moves an object to be moved with high accuracy, and a suitable braking apparatus provided on said drive unit.
2. Description of the Prior Art
An example of this type of drive unit of the prior art is shown in FIG. 1.
As shown in the drawing, this drive unit has a guiding device comprising a long base member 1 acting as a guiding member, and a slider in the form of moving body 2 which moves along said base member 1. More specifically, a plurality of rollers (not shown) are provided in moving body 2, and these rollers roll over a track formed along the lengthwise direction in base member 1.
Overhang 1a is formed on one side of base member 1, and a detected element in the form of linear scale 4 is provided on said overhang 1a roughly over its entire length. In contrast, small bracket 2a is provided on the side of moving body 2, and detection elements in the form of light emitting element 5a and light receiving element 5b are mounted on said small bracket 2a. This linear scale 4, light emitting element 5a and light receiving element 5b compose a position detection device for detecting the position of moving body 2 with respect to a track rail in the form of base member 1.
On the other hand, a direct current linear motor, which composes a drive unit together with the above-mentioned guiding device, is composed in the manner described below.
As shown in the drawing, said direct current linear motor is composed of a primary side equipped with a large number of armature coils 7, arranged in a row on base member 1 in the lengthwise direction of said base member 1, and a secondary side having a field magnet (not shown) attached to the bottom surface of moving body 2 to oppose each of said armature coils 7. Each armature coil 7 is wound into the shape of a rectangular loop, attached to coil substrate 8, and fastened together with said coil substrate 8 to base member 1 by screws 9. In addition, the above-mentioned field magnet is magnetized by alternately arranging a plurality of N and S magnetic poles along the direction in which moving 2 is to move, namely the lengthwise direction of base member 1.
In the above-mentioned drive unit, by supplying a prescribed current to armature coils 7, thrust is produced based on Fleming's right hand rule between the primary and secondary sides. For example, if base member 1, to which the primary side is coupled, is taken to be the stationary side, moving body 2 integrated into a single unit with the secondary side is moved by this thrust. The position of moving body 2 with respect to base member 1 is then detected by the position detection device previously described.
The drive unit having the constitution described above is able to move and position a moving portion consisting of the secondary side of a linear direct current motor and a moving body 2 and so forth to a desired position with high accuracy. However, since said positioned moving portion only stops using magnetic force for the braking force, it is unstable under conditions such as being subjected to vibrations and so forth from the outside, thus having the disadvantage of it being difficult to stop without making fine movements to the prescribed position. In addition, since braking by magnetic force acts relatively slowly with respect to the inertia of the moving portion, this unit has the disadvantage of being unable to stop suddenly even when so required. In addition, in the case electrical power was to be cut off during operation of the drive unit caused by a power outage and so forth, since the moving portion would travel by inertia without any action of braking force whatsoever, it is necessary to stop said drive unit immediately in order to avoid collision with other equipment and so forth.